Spinal Cord Injury Center, Heidelberg University Hospital, Heidelberg, Germany.
Department of Physical and Theoretical Chemistry, University of Regensburg, Regensburg, Germany.
Acta Biomater. 2015 Nov;27:140-150. doi: 10.1016/j.actbio.2015.09.001. Epub 2015 Sep 5.
Despite recent progress in enhancing axonal growth in the injured spinal cord, the guidance of regenerating axons across an extended lesion site remains a major challenge. To determine whether regenerating axons can be guided in rostrocaudal direction, we implanted 2mm long alginate-based anisotropic capillary hydrogels seeded with bone marrow stromal cells (BMSCs) expressing brain-derived neurotrophic factor (BDNF) or green fluorescent protein (GFP) as control into a C5 hemisection lesion of the rat spinal cord. Four weeks post-lesion, numerous BMSCs survived inside the scaffold channels, accompanied by macrophages, Schwann cells and blood vessels. Quantification of axons growing into channels demonstrated 3-4 times more axons in hydrogels seeded with BMSCs expressing BDNF (BMSC-BDNF) compared to control cells. The number of anterogradely traced axons extending through the entire length of the scaffold was also significantly higher in scaffolds with BMSC-BDNF. Increasing the channel diameters from 41μm to 64μm did not lead to significant differences in the number of regenerating axons. Lesions filled with BMSC-BDNF without hydrogels exhibited a random axon orientation, whereas axons were oriented parallel to the hydrogel channel walls. Thus, alginate-based scaffolds with an anisotropic capillary structure are able to physically guide regenerating axons.
After injury, regenerating axons have to extend across the lesion site in the injured spinal cord to reestablish lost neuronal connections. While cell grafting and growth factor delivery can promote growth of injured axons, without proper guidance, axons rarely extend across the lesion site. Here, we show that alginate biomaterials with linear channels that are filled with cells expressing the growth-promoting neurotrophin BDNF promote linear axon extension throughout the channels after transplantation to the injured rat spinal cord. Animals that received the same cells but no alginate guidance structure did not show linear axonal growth and axons did not cross the lesion site. Thus, alginate-based scaffolds with a capillary structure are able to physically guide regenerating axons.
尽管最近在增强损伤脊髓中的轴突生长方面取得了进展，但引导再生轴突穿过延长的损伤部位仍然是一个主要挑战。为了确定再生轴突是否可以在头尾方向上被引导，我们将长 2 毫米的基于藻酸盐的各向异性毛细血管水凝胶植入大鼠脊髓 C5 半切损伤中，该水凝胶中种植了表达脑源性神经营养因子（BDNF）或绿色荧光蛋白（GFP）的骨髓基质细胞（BMSC）作为对照。损伤后 4 周，大量 BMSC 存活在支架通道内，伴随有巨噬细胞、施万细胞和血管。对进入通道的轴突进行定量分析表明，与对照细胞相比，表达 BDNF 的 BMSC （BMSC-BDNF）种植的水凝胶中有 3-4 倍的更多轴突。通过整个支架延伸的顺行追踪轴突的数量在 BMSC-BDNF 支架中也显著更高。将通道直径从 41μm 增加到 64μm 不会导致再生轴突数量的显著差异。没有水凝胶的 BMSC-BDNF 填充的损伤表现出随机的轴突方向，而轴突则平行于水凝胶通道壁取向。因此，具有各向异性毛细血管结构的藻酸盐支架能够物理引导再生轴突。
受伤后，再生轴突必须穿过损伤的脊髓中的损伤部位延伸，以重新建立丧失的神经元连接。虽然细胞移植和生长因子递送可以促进损伤轴突的生长，但如果没有适当的引导，轴突很少延伸穿过损伤部位。在这里，我们表明，填充表达促生长神经营养因子 BDNF 的细胞的线性通道的藻酸盐生物材料在移植到损伤的大鼠脊髓后促进整个通道中的线性轴突延伸。接受相同细胞但没有藻酸盐引导结构的动物没有表现出线性轴突生长，并且轴突没有穿过损伤部位。因此，具有毛细血管结构的藻酸盐支架能够物理引导再生轴突。
